You can get your mat object information (dimmension, rows, cols, size ....) and resize, reshape, copy Mat object by using Mat class method. 1. Get Information of Mat object cout << "dimmension : " << mat7 . dims << endl; cout << "rows : " << mat7 . rows << endl; cout << "columns : " << mat7 . cols << endl; cout << "size : " << mat7 . size () << endl << endl; cout << "number of total elements: " << mat7 .total() << endl; cout << "type :" << mat7 .type() << endl; cout << "depth :" << mat7 .depth() << endl; cout << "channels :" << mat7 .channels() << endl; 2. Resize Mat object Mat_ <int> mat10( 2 , 4 ); mat10 << 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ; mat10 .resize( 1 ); // resize to one row mat10 .resize( 2 ); // resize to two rows mat10 .resize( ...